DC area home prices rose 10.7 percent in January, and it was the fourth month in a row that prices increased by double digits.

A report released today by RealEstate Business Intelligence (RBI) revealed that the median home price for the area in January was $343,200, almost 11 percent higher than one year ago. Prices rose by double digits (year-over-year) in six of the eight jurisdictions covered in the region. In DC proper, prices rose 12.3 percent, from $375,000 to $421,000.

The main force putting upward pressure on prices is a familiar trend for area home buyers: low inventory.

Like December, there were over 4,000 fewer active listings at the end of January 2013 than in January 2012. The total number of new listings added in the area last month (4,004) was the lowest for any January in over 15 years.

While sellers may continue to sit on the sidelines, buyers are as active as ever. Contract activity rose 26.4 percent month-over-month, well above the 10-year December-to-January average of 16.9 percent. The property category leading the way in January was condos, where the contract activity was 10.3 percent higher than a year earlier.

Another interesting takeaway from RBI’s report: Arlington County was the one jurisdiction where prices fell year-over-year. RBI gave the following explanation for the drop in prices:

“It is more reflective of the type of properties available than softening demand. Condos made up 55.1 percent of all sales in the County in January 2013 compared to 48.3 percent this time last year, and these properties tend to have lower price points.”

The area that RBI analyzes includes DC, Montgomery County, Prince George’s County, Alexandria City, Arlington County, Fairfax County, Fairfax City, and Falls Church City.